With display devices, there is the difficulty that as a rule the position of the coupling-out section cannot be changed in the horizontal direction or relative to a first lateral end of the front section because otherwise the image guidance in the spectacle lens and the necessary coupling-out is optically significantly impaired.
Furthermore, there is the further difficulty that the size of the eyebox (the area in which the user's eye can move and he can still see the generated image as a virtual image) provided by the imaging optical system has an extent in the horizontal direction (i.e. in a direction from the first to a second lateral end of the front section) of approx. 5 mm. For a good possibility of perceiving the virtual image, it is therefore necessary for the eyebox (or the exit pupil of the imaging optical system) to be made to cover the pupil of the user's eye as completely as possible when the holder is fitted on the head.
Because of the anatomical differences between different users, however, as a rule the distance from temple to pupil of the eye and the interpupillary distance is different, with the result that it is difficult to reliably achieve this coverage in the case of different users.